The long-term goal of the proposed research is to understand the molecular mechanisms involved in the replication of chromosomes in eukaryotic cells, particularly the mechanisms that regulate DNA replication during the cell cycle. This goal is a fundamental aspect of the more general objectives of the Program to understand the basic mechanisms that control cell growth and maintain genomic stability. Our approach to this problem involves genetic and biochemical studies of the initiation of DNA replication in the model organism Schizosaccharomyces pombe. We plan to focus our efforts in two general areas. First, we will continue our biochemical studies to identify, purify and characterize initiator proteins and to define their interactions with origins of DNA replication. Second, we will study how the initiation of DNA replication is regulated by the specific phosphorylation of cellular initiation proteins.